Filter element and method for the production thereof

ABSTRACT

The invention relates to a filter element comprising a filter cylinder whose outer side rests against a fluid-permeable supporting tube ( 15 ). The inside ( 3 ) of the filter cylinder can be flown through by the fluid to be filtered, and the filter cylinder is formed by a filter mat web. The filter mat web has a series of folds ( 9 ) that rest against one another at least in areas. Both ends of the filter mat web are joined to one another at a junction ( 5 ) in order to form an annolar body ( 1 ). The inventive filter element comprises a device that acts upon the junction ( 5 ) in order to prevent, in the area of the junction ( 5 ), a bulging of the folds ( 9 ) that is caused by the flow of the fluid.

The invention relates to a filter element having a filter cylinderadjoining on its exterior a fluid-permeable support tube through whichfilter cylinder fluid to be filtered may flow and which is made up of afilter mat web which has a sequence of folds adjacent to each other atleast in individual areas and the two ends of which are joined to eachother at a connecting point in order to form an annular element. Theinvention also relates to a method for the production of such a filterelement.

Filter elements of the type indicated in the foregoing are available onthe market and are widely used, for example, in hydraulic assemblies inbranches of a system through which hydraulic fluids flow. The knownfilter elements are not entirely satisfactory with respect to theirsafety in operation and the beta value stability of decisive importancefor filter output. With high fluid outputs in particular, the dangerexists that deformation or damage may occur at the junction point atwhich the ends of the filter mat web are joined to form the annularelement forming the filter cylinder as a result of the differentialpressure of the fluid which acts on the junction point. Such damageand/or deformation of the folds in the area of the junction point arehere identified by the common expression Afold bulging.@

The object of the invention is to create a filter element characterizedby operating safety and beta value stability which are better than thosein the state of the art, even with high flow output.

In the case of one filter element of the type indicated in theforegoing, this object is attained by means of a configuration at thejunction point acting to prevent a bulging of the folds in the area ofthe junction point caused by the action of fluid flow.

In that, as claimed for the invention, special protective measures havebeen taken at the point of junction of the filter mat web, which preventbulging of the folds in this area, the desired improvement in operatingsafety is achieved even in the event of high flow output andcorrespondingly high fluid differential pressures in the area of thejunction point.

In one preferred exemplary embodiment, the configuration preventingbulging in the area of the junction point is formed in that the folds ofthe filter mat web are joined to each other along those end edges, whichface the interior of the annular element to be formed, so that bothfolds adjacent to each other at the junction point have their topspositioned on the exterior on the annular element and facing the supporttube. In that the junction point, that is, the fusion seam or area ofadhesion by means of which the annular element forming the filtercylinder is closed, is positioned in the interior on the filtercylinder, the junction point on both sides rests on the support tube byway of the adjacent folds, the tops of which are positioned on theexterior on the annular element. In this configuration the junctionpoint forms no point weak in resisting the active forces resulting fromthe differential pressure applied in operation.

By preference, the filter mat web is in the form of a flexible matstructure of metal-free plastic-supported filter mats, connection of theends of the filter mat web, so that a closed annular structure isformed, being effected by means of a fusion seam. In order to makesimple and efficient production possible, the fusing process must becarried out on the exterior of the annular element, that is, thejunction point is positioned on the exterior of the filter cylinder sothat, as stated earlier, the fusion seam would form a weak point of thefilter cylinder during operation.

In order to make allowance for this factor, provision is made by theinvention for an especially advantageous exemplary embodiment such thatthe dimensions determined for the flexible filter mat web are such thatthe annular element may be reversed after formation of an exteriorfusion seam, so that the fusion seam is now positioned on the interioron the reversed annular element now ready for use.

Despite the simplicity of the production method, that is, formation of afusion seam on the exterior, the annular element forming the filtercylinder after reversal is protected as desired from bulges in the areaof the fusion seam now positioned in the interior.

In place of the protection from bulges resulting from the positioning ofthe junction point in the interior, or in addition to this protection,it is claimed for the invention that the configuration preventingbulging may have in the area of the junction point a retaining devicewith retaining elements which overlap the folds of the annular elementadjoining the junction point on both sides, on the side of the foldsfacing away from the junction point. Especially secure support of thefolds in the area of the junction point is thereby ensured.

The retaining elements of the retaining device may be in the form of aretaining projections formed on the inside of the support tube andprojecting radially inward.

As an alternative, the retaining elements may be in the form of legs ofa clamping element U-shaped in cross-section, which may be inserted ontothe folds adjacent to the junction point of the annular element.

Another object of the invention is provision of a process for productionof the filter element, the characteristics of this process beingspecified in claim 10.

The invention will be described in greater detail below with the aid ofexemplary embodiments illustrated in the drawings in which:

FIG. 1 shows a top view of an annular element provided for a filterelement as claimed for the invention, in the partly completed state, afusion seam formed on the annular element from the exterior beingpositioned on the exterior;

FIG. 2 is a top view similar to that of FIG. 1, showing the annularelement forming the filter cylinder in the finished state, that is, withthe fusion seam positioned on the exterior after reversal;

FIG. 3 is a perspective view of the annular element of FIG. 2;

FIG. 4 is a perspective view of the filter disk formed in the course ofreversal of the annular element shown in FIG. 1;

FIG. 5 is a greatly enlarged representation of a fold section of theannular element, along with data indicating the dimensions;

FIG. 6 is a cross-section of a second exemplary embodiment of the filterelement claimed for the invention;

FIG. 7 is a perspective view of the support tube of the exemplaryembodiment shown in FIG. 6 less the filter cylinder present in thissupport tube, and

FIG. 8 a perspective exploded view of a third exemplary embodiment ofthe filter element.

Reference is made to FIGS. 1 to 5, which illustrate a first exemplaryembodiment of the filter element claimed for the invention, theconventionally configured support tube not being shown in these figures.When the filter cylinder is in the finished state, it is enclosed inthis support tube, and is designated as a whole as 1, while in the formshown in FIGS. 2 and 3 it has been introduced into the support tube,which is not shown. During operation, filter fluid-flows through theinterior of the annular element indicated in FIGS. 2 and 3; that is, theclean side of the filter device (not shown) having the filter elementclaimed for the invention is situated on the exterior of the supporttube enclosing the annular element 1.

As shown in the figures, the annular element 1 is in the form of afolded filter mat web, which is joined at its two ends to form a closedring, the junction point being configured as a fusion seam 5. In theexemplary embodiments described here, the filter mat web is in the formof a flexible mat structure possessing resilient properties, moreprecisely in that of metal-free plastic-supported filter mats which maybe fused together by a fusion seam 5 extending longitudinally to producethe annular element 1.

By preference a six-layer structure of the filter mat web is providedwhich has the following layers in sequence: an exterior support, aprotective nonwoven layer, a prefilter layer, a main filter layer, anonwoven support layer, and an interior support. A polyamide grid or apolyester fabric may be considered for the exterior support. A polyestermaterial may be provided as the protective nonwoven layer. A glass fibermaterial, preferably in reduced form with respect to thickness and baseweight, or a meltblown material may be considered for the filter layer.The main filter layer may analogously be a glass fiber material, whichoptionally is impregnated, or a meltblown material. A polyester orpolyamide material may in turn be used as the support nonwoven layer,which may also be represented by a viscose nonwoven material or apolyamide with meltblown material. The interior support may, like theexterior support, be configured as a grid or fabric based on a polyamideor polyester basis.

As is shown by comparison of FIGS. 1 to 4, this fusion seam 5 isdisplaced to the interior in the finished state shown in FIGS. 2 and 3by reversal of the annular element 1 from the initial state illustratedin FIG. 1, in which the fusion seam 5 is positioned on the exterior,that is to say, is in the form of a lengthwise seam made on the outside.While in the state shown in FIG. 1, with fusion seam 5 positioned on theexterior, on the outer edge of the annular element 1, a gap 7 exists inthe area of which there is no contact between the tops 11 of the folds 9immediately adjacent to the fusion seam 5 on both sides and theenclosing support tube (not shown), in the state shown in FIGS. 2 and 3the tops 11 of the folds 9 immediately adjacent to the fusion seam 5 arepositioned on the outside (see FIG. 2) and accordingly are positionedadjacent on the support tube.

While in the case of the state shown in FIG. 1 there exists at thedifferential pressure prevailing during operation the danger of bulgingin the area of the fusion seam 5, which may be moved radially outward bypressure forces, tensile forces being active on the fusion seam 5, whichtend to tear the seam open, in the case of the reverse state illustratedin FIGS. 2 and 3, neither is bulging as a result of radial movement ofthe fusion seam 5 possible, since the adjacent fold top 11 is supported,nor is the fusion seam 5 subject to load application in the form offorces of pressure tending to effect separation.

FIGS. 4 and 5 serve to illustrate the configuration and determination ofthe dimensions of the filter mat web forming the annular element 1, thatis, a configuration which permits reversal of the annular element. Themaximum length of the annular element, which permits reversal if it isin the form of a flexible fold structure, depends on the number offolds, the height of the folds, the strength of the mat structure, andthe thickness of the folds of the annular element. FIG. 4 illustratesthe exterior and interior diameters of the disk element 13 which aretemporarily obtained in the course of reversal of the annular element 1.FIG. 5 illustrates determination of the dimensions of the folds 9 withrespect both to strength of the material and to the fold size.

The maximum length of the annular element may be determined as followson the basis of the parameters entered in FIGS. 4 and 5:

-   F_(ANZ)=number of folds-   F_(H)=height of fold-   F_(D)=thickness of fold-   M=strength of material of mat structure-   L_(M)=extended length of filter web-   L_(Mmax)=maximum extended length of filter web-   D_(amax)=maximum external diameter of filter disk-   D_(i)=internal diameter of filter disk-   L_(max)=maximum length of filter cylinder $\begin{matrix}    {L_{M} = {2^{*}F_{Ans}*\left( {F_{H} - {2^{*}M} + \frac{\pi^{*}M}{2}} \right)}} & \left. 1 \right) \\    {D_{a_{\max}} = {D_{i} + {2^{*}L_{\max}}}} & \left. 2 \right) \\    {L_{\max} = \frac{D_{a_{\max}} - D_{i}}{2}} & \left. 3 \right) \\    {D_{i\quad 2} = \frac{F_{Ans}*F_{D}}{\pi}} & \left. 4 \right) \\    {L_{M_{\max}} = {D_{a_{\max}}*\pi}} & \left. 5 \right) \\    {D_{a_{\max}} = \frac{L_{M_{\max}}}{\pi}} & \left. 6 \right) \\    {D_{a_{\max}} = {D_{i} + {2*L_{\max}}}} & \left. 7 \right) \\    {L_{\max} = \frac{D_{a_{\max}} - D_{i}}{2}} & \left. 8 \right) \\    \left. {\left. {L_{\max} = {\frac{\frac{L_{M_{\max}}}{\pi} - D_{i}}{2}8}} \right)\quad{mit}\quad 6} \right) & \left. 9 \right) \\    \left. {\left. {L_{\max} = {\frac{L_{M_{\max}} - {F_{Ans}*F_{D}}}{2*\pi}9}} \right)\quad{mit}\quad 4} \right) & \left. 10 \right) \\    {\left. {\left. {L_{\max} = {\frac{F_{Ans}*\left( {F_{H} - {2*M} + \frac{\pi*M}{2} - \frac{F_{D}}{2}} \right)}{\pi}10}} \right)\quad{mit}\quad 1} \right)\left\lbrack {{mit} = {{with}\quad{value}\quad{of}}} \right\rbrack} & \left. 11 \right)    \end{matrix}$

FIGS. 6 and 7 illustrate a second exemplary embodiment of the filterelement claimed for the invention. Unlike the preceding example thesupport tube 15 enclosing the filter cylinder is shown, this supporttube 15 being shown separately in FIG. 7, that is, without the filtercylinder inserted. As is clearly shown in FIG. 7, the support tube 15,which is of transfer-molded plastic, has on the exterior, which in afilter device as claimed for the invention adjoins the clean side, hasstrips 17 extending longitudinally which are connected by webs 19forming annular elements between which are apertures 21 as fluidpassages. As shown in FIG. 6, when a filter cylinder has been insertedinto the support tube 15, the area adjacent to the fusion seam 5 on bothsides is secured by a retaining device having retaining projections 23and 25, which overlap the folds of the annular element, which areadjacent to the fusion seam on both sides, on the sides of the foldsfacing away from the fusion seam 5 (see FIG. 6).

As shown in FIG. 7 in particular, the retaining projections 23 and 25are integrally molded on the inside of the support tube 15, a retainingprojection 23 being configured to extend along and through a strip 17 ofthe support element, while divided retaining projections 25 are providedon the other side between which are interstices 27 corresponding to theapertures 21 forming the fluid passages. With the enclosure of the areaof the fusion seam 5 formed by the retaining projections 23 and 25effective protection is obtained from the danger of bulging in the areaof the junction point.

FIG. 8 shows a third exemplary embodiment having a support tube 15without interior retaining projections 23 and 25. In place of theenclosure of the area of the junction point, that is, the fusion seam 5,there is provided in this exemplary embodiment a retaining device havinga metal clamping element 31 U-shaped in cross-section which may bepositioned by way of insertion on the sides facing away from the fusionseam 5 and the retaining action essentially corresponds to that of theretaining projections 23 and 25 of the preceding exemplary embodiment.

In addition, in the example shown in FIG. 8, the annular element 1 hasbeen reversed to assume the state shown in FIG. 2, so that the fusionseam 5 is positioned in the interior and the tops of the folds adjoiningthis seam are supported directly by the support tube 15. Consequently,this exemplary embodiment is protected in two ways from bulging in thearea of the fusion seam 5.

1. a filter element which has a filter cylinder adjacent to afluid-permeable support tube (15) through which filter cylinder thefluid to be filtered may flow from its interior and which is in the formof a filter mat web having a series of folds (9) adjacent to each otherat least in individual areas and the two ends of which are connected toeach other at a junction point (5) for formation of an annular element(1), characterized by a configuration effective at the junction point(5) in preventing bulging of the folds (9) in the area of the junctionpoint (5) as a result of flow of fluid.
 2. The filter element as claimedin claim 1, wherein a configuration preventing bulging in the area ofthe junction point (5) is formed in that the respective folds (9) of thefilter mat web on the ends are joined to each other along the end edgeswhich face the inside (3) of the annular element (1) to be formed, sothat the two folds (9) adjoining the junction point (5) are positionedwith their crowns (11) on the outside on the annular element (1) andfacing the support tube (15).
 3. The filter element as claimed in claim2, wherein the filter mat web is in the form of a flexible mat structureof metal-free plastic-supported filter mats.
 4. The filter element asclaimed in claim 3, wherein the connection of the ends of the filter matweb is in the form of a fusion seam (5).
 5. The filter element asclaimed in claims 3, wherein the dimensions determined for the flexiblefilter mat web are such that, after formation of an exterior fusion seam(5) joining the filter mat web, the annular element (1) may be reversedso that the fusion seam (5) is in the interior on the reversed annularelement (1).
 6. The filter element as claimed in claims 1, wherein theconfiguration preventing bulging in the area of the junction point (5)has a retaining device which has retaining elements (23, 25), whichoverlap the adjacent folds (9) on both sides of the annular element (1)on the sides of such folds facing away from the junction point (5). 7.The filter element as claimed in claim 6, wherein the retaining elementsare in the form of retaining projections (23, 25) which are configuredto project radially inward on the inside of the support tube (15). 8.The filter element as claimed in claim 7, wherein the support tube (15)is configured as a transfer-molded plastic component with retainingprojections (23, 25) of the retaining device integrated with it.
 9. Thefilter element as claimed in claim 6, wherein the retaining elements arein the form of the legs of a clamping element (31) U-shaped incross-section, it being possible to insert such clamping element ontothe folds (9) adjacent to the junction point (5) of the annular element(1).
 10. A process for production of a filter element as claimed inclaim 1, characterized in that a filter cylinder adjoining afluid-permeable support tube (15) is formed on the exterior of suchfilter element by joining together a flexible filter mat web havingseries of folds adjacent to each other at least in individual areas onits end edges to form an annular element (1) and joined along a junctionpoint (5) positioned on the exterior of the annular element (1), and inthat the annular element (1) formed is reversed so that the junctionpoint (5) is in contact with it in the interior.